The disposal of residential area waste and also industrial wastes is a problem in view of the sustainability which is being increasingly demanded politically. The routes taken hitherto, namely reducing amounts of waste by avoiding waste and introducing separate collection of valuable materials have had initial success. For the remaining wastes which consist essentially of a three-component mixture of inert substances, organic matter and water and which cannot be supplied to direct exploitation, proposals have already been made in WO 2005/051547 [U.S. Pat. No. 7,469,846]. In order to generate fractions which can be exploited materially and/or energetically, and to largely avoid landfill, a wet-mechanical treatment is proposed of compositions of matter which consist of inert substances, water and also organic substances having a water-soluble and biologically convertible fraction, wherein first the composition of matter is continuously mixed in a mixer with water as separation and washing agent, without separating the components of the mixture until a dry matter content to 15% to 25% is established. Hereafter, in a first stage, the composition of matter is discharged from the mixer using a conveyor, wherein, owing to the addition of water, the light components remain dissolved in a solid-liquid mixture having a dry matter content of 10% to 20%, whereas the heavy components settle and are separated by the conveyor as the first heavy inert fraction having a particle size >25 mm. Light organic substances having a particle size of 30 mm to 120 mm are sieved off from the remaining solid-liquid mixture as first organic light fraction, rinsed and pressed. This fraction can if appropriate after a drying be exploited energetically by combustion or gasification, if, when the corresponding limiting values are kept, material exploitation in agriculture does not come into consideration.
In a second stage, inert heavy substances having a particle size of 2 mm to 25 mm are first separated off from the remaining suspension having an adjusted dry matter content of 6% to 12% by gravity and subsequently further organic light substances of a particle size of 3 mm to 30 mm are separated off by sieving and washing. The organic fraction sieved off here can likewise be washed with water and pressed off.
In a third stage, further inert heavy substances of a particle size <2 mm are separated off from the remaining suspension having an adjusted dry matter content of 3% to 8% by centrifugal forces and thereafter further organic light substances of a particle size of 150 μm to 3 μm are separated off by sieving and washing. The filter cake which is formed in fine sieving may likewise be pressed off and used, for example in agriculture, as fertilizer or as soil improver, for which reason the organic matter is either composted in composting units or fermented in fermentation units and composted or dried and used as loose compost bed or as fertilizer.
In the further processing of organic compositions of matter which contain not only fossil but also native organic matter, the present invention makes a start.
According to the prior art, extrusion is known in plastics processing and for shredding of organic substances. Thus in DE 44 44 745, a method is described for producing high-grade plant substrate from precomminuted wood or wood wastes containing effluent sludge, liquid manure sludge, sewage sludge or biowaste using a screw extruder, in which the substances are continuously fed into the screw extruder at such a throughput that the wood and coarser components are shredded and intensively mixed with the additives at temperatures of above 100° C. The temperatures set are intended to ensure that pathogens, bacteria, viruses, spores or weed seeds are killed, an excessive water content is vaporized and a material emerges at the extruder head which is substantially aseptic and is of a structure which is particularly readily suitable as plant substrate.
DE 10 2004 054 468 A1 describes a method of anaerobic fermentation of plant substrates for producing biogas, in which, to achieve a detectably higher gas formation rate, upstream of the fermentation process there should be connected a preparation prestage by extrusion of the plant substrates outside the reactor, in such a manner that a high-grade homogenized biomass is formed, the cell structure of which is substantially destroyed. By targeted surface enlargement of the biogenic material, a more rapid nutrient availability for the methanogens should be achieved. When a double-screw extruder is used, in the flank regions of the screw shafts in the encapsulated and armored device, pressure conditions and temperature conditions are formed which are able to destroy explosively the cell structure of plant material and/or biomass. Here, pressures above 5×106 Pa and temperatures >120° C. are possible. It is a problem in these conditions that, for instance, plastics present in the material quantity stick together and form agglomerates which make subsequent separation of matter difficult. The method described in the publication, in addition, cannot be carried out without pretreatment of the starting materials, since without prior separation of inert matter, i.e. in particular the removal of stones, gravel, sand and metals, high wear of the plant must be accepted. A possible suitable pretreatment is described by the above cited WO 2005/051547 A1.